Heat-resistant Ti alloys such as TiAl intermetallic compounds and Ti alloys; superalloys such as Ni-based, Nb-based, Ir-based, and Re-based superalloys; carbon materials; and a variety of intermetallic compounds are used as structural materials exposed to a high-temperature atmosphere, such as turbochargers, jet engines, and gas turbines. Among them, Ni-based alloys, and Ni—Cr-based alloys such as Ni—Cr binary alloys mainly composed of Cr and Ni—Cr multicomponent alloys containing other alloying elements are applied to gas turbines, jet engines, chemical plants, and the like because of high strength and high creep resistance at high temperatures.
The high-temperature atmosphere that the heat-resistant material is exposed to may contain oxidizing or corrosive components such as oxygen, steam, and the like. When the heat-resistant material is exposed to a corrosive and high-temperature atmosphere, the heat-resistant material is easily susceptible to oxidization and high-temperature corrosion caused by reactions with the corrosive components in the atmosphere. When O, N, S, Cl, H, C, or the like in the atmosphere penetrates the heat-resistant material, internal corrosion may occur in the heat-resistant material surface, decreasing the strength of the material.
The high-temperature oxidation and high-temperature corrosion of the heat-resistant material are prevented by coating the surface of the heat-resistant material with a protective film having a high atmospheric blocking capability (for example, Patent Documents 1 to 8). A typical protective film is composed of Al2O3, which is formed on a heat-resistant material surface by diffusing Al to the surface from the base metal of the heat-resistant material in an oxidizing atmosphere, chemical vapor deposition (CVD), thermal spraying, reactive sputtering, or the like. The Al2O3 film prevents the metal components in the heat-resistant material from reacting with oxidizing agents in the atmosphere and maintains the original excellent high-temperature characteristics of the heat-resistant material.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 3-44484    Patent Document 2: Japanese Unexamined Patent Application Publication No. 5-195188    Patent Document 3: Japanese Unexamined Patent Application Publication No. 10-183373    Patent Document 4: Japanese Unexamined Patent Application Publication No. 2000-192258    Patent Document 5: Japanese Unexamined Patent Application Publication No. 2001-81577    Patent Document 6: Japanese Unexamined Patent Application Publication No. 2001-192887    Patent Document 7: Japanese Unexamined Patent Application Publication No. 2001-295076    Patent Document 8: Japanese Unexamined Patent Application Publication No. 2001-355081